Why knowledge is NOT “justified true belief”

In Theaetetus, Plato’s Socrates argues that knowledge is “justified true belief”. That is, it is, a belief for which the believer has a justification and that is, in fact, true (see en.wikipedia.org/wiki/Epistemology). This doesn’t really work.

Firstly defining knowledge as belief excludes tacit knowledge, such knowing how to ride a bicycle. My ability to ride a bicycle does not depend upon my having any particular beliefs about riding or, indeed, bicycles. So Socrates’ definition can only apply to explicit knowledge.

To see why it doesn’t even work for explicit knowledge consider the following truth table for beliefs.

	1	2	3	4
Is the belief justified?	Y	Y	N	N
Is the belief true?	Y	N	Y	N
Does it meet Socrates’ definition?	Y	N	N	N

Justification: I agree with Socrates in wanting to distinguish knowledge from mere guesswork. To count as knowledge a belief needs to be justified. Suppose you believe that Hungary is an attractive market for your latest product. This is a justified belief if you can produce evidence for it. I would accept market research and the success of similar products as sufficient evidence so if you have that data I’ll accept your belief as justified. I’m prepared to agree that a belief is justified even if the evidence is not conclusive, as it won’t be in this case until you’ve tried to sell it in Hungary.

Truth: The problem comes in distinguishing cases 1 and 2 in the table. Is your belief about the Hungarian market true? The only way that I can know this is to wait for the results of your Hungarian launch. And if you never launch your product in Hungary then neither of us will ever know if your belief was true – and therefore knowledge. This is inconvenient but not absurd.

How about the market research? Is that knowledge, ie is the data you have accurate and appropriate? You believe so and you have reasons for doing so, eg that you used a reputable firm with experience of the Hungarian market. You certainly have a justified belief. But can you know that it’s true? You cannot be certain, so this, also, does not meet Socrates’ definition of knowledge.

Not truth but confidence

The reality here is that beliefs can be held varying degrees of confidence. We can rarely be certain but are often, justifiably, confident. And we determine the proper degree of confidence using just those arguments that constitute the justification for the belief.

So knowledge, I suggest, is those beliefs where the arguments and evidence in favour make them seem more likely than not. Beliefs where the arguments and evidence in favour fall short of that are rumours, opinions or prejudices.

This view has two immediate consequences:

• In applying knowledge we should consider how sure we are of its truth. We should not claim certainty where the evidence is doubtful.
• Systems that store knowledge should include assessments of reliability and/or pointers to the sources of the supposed knowledge.